Abstract
Reduced knee flexion is a leading feature of post-stroke gait, but the causes have not been well understood. The purpose of this study was to investigate the relationship between the knee flexion and the lower-limb muscle activation within the stance-to-swing phases of gait cycle in the post-stroke hemiplegic patients. Ten stroke patients and 10 age- and gender-matched healthy subjects participated in the experiment. The lower-limb kinematic signals and the surface electromyography (sEMG) signals of the left and right rectus femoris (RF), biceps femoris (BF) and lateral gastrocnemius (GS) were recorded during walking. The angle range (AR) of knee flexion, the root mean square (RMS) and the mean frequency (MNF) of sEMG signals were calculated from the terminal stance (TSt) to the initial swing (ISw) phases of gait cycle. Stroke patients showed lower bilateral AR of knee flexion and lower RMS of GS on the paretic side, but higher MNF of RF on the non-paretic side compared with the controls. Within the stroke patients, significant differences were found between their paretic and non-paretic limbs in the AR of knee flexion, as well as in the RMS and MNF of GS (p < 0.05). Regression analysis showed that the RMS of BF, MNF of BF and MNF of GS explained 82.1% of variations in AR of knee flexion on paretic side (r2 = 0.821). But the RMS and MNF of all the muscles (including the RF, GS and BF) could explain 65.6% of AR of knee flexion variations on the non-paretic side (r2 = 0.656), and 45.2% of variations for the healthy subjects (r2 = 0.452). The reduced knee flexion during gait was associated with altered magnitude and frequency of muscle contractions and with simplified muscle synergy in the post-stroke hemiplegic patients. Identifying the muscles that are responsible for knee stiffness may facilitate improvement of rehabilitation strategy for post-stroke gait.
Highlights
Recovery of locomotion ability is a primary goal of post-stroke hemiparesis rehabilitation
No significant difference was found in mean frequency (MNF) of GS between the paretic side and the controls (p = 0.081) or between the non-paretic side and the controls (p = 0.883) (Fig 5B)
Results of the root mean square (RMS) and MNF showed that the stroke affected the magnitude and frequency of the surface electromyography (sEMG) signals for the GS, but not for the biceps femoris (BF) (Fig 5)
Summary
Recovery of locomotion ability is a primary goal of post-stroke hemiparesis rehabilitation. The abnormal gait after stroke is characterized by reductions in stride length, movement speed, muscle power and joint range of motion [1,2,3]. All the lower-limb joints could be affected by stroke, the knee would be more vulnerable than the others. The peak knee flexion in the swing phase of gait usually drops off, recognized as the stiff-knee gait, which is a common abnormality associated with stroke. No consensus has been reached regarding the pathophysiology of stiff-knee gait. Identifying the contributors to the stiff knee may facilitate to find more efficient rehabilitation strategy for post-stroke gait
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